High voltage transmission and distribution lines are typically strung between a series of spaced-apart support towers or poles. The conductors are connected to insulators mounted or suspended from crossarms extending at the upper end of transmission or distribution poles, or conductor support points built into transmission towers. Periodically it is necessary to replace or repair the poles or towers, crossarms and insulators to maintain the electrical circuit in good working order. It is preferable if this maintenance and repair work can be performed without de-energizing the conductors in order to avoid the necessity of purchasing power from an alternative source, or other system disruptions.
Hot line repair work is a potentially hazardous undertaking. Safety regulations require that linemen maintain a minimum work clearance or “limit of approach” from energized conductors. The limit of approach varies depending upon the voltage of the conductors in question.
Conventional procedures used by linemen to temporarily support energized conductors in order to enable repair of damaged or obsolete components involve the use of insulated wire tongs, lift poles and rope blocks in labor-intensive, complex rigging arrangements. Conventional fiberglass insulated tools are limited to use only in good weather. Any accumulation of moisture which may impair their insulating property requires that the job be stopped, and that all and that the conductors be placed in an insulator which is rated for all-weather use.
Several auxiliary crossarms have also been proposed in the past for temporarily supporting conductors, thereby reducing the need for labor-intensive “stick work” by linemen. For example, U.S. Pat. No. 4,973,795, which issued to Sharpe on Nov. 27, 1990, relates to an auxiliary crossarm consisting of an insulated boom fitted with polymer insulators and conductor hooks for releasably engaging energized conductors. The Sharpe boom is suspended from a crane above the transmission lines to be serviced.
Auxiliary crossarms for temporarily lifting and supporting energized conductors from below are also well-known. Such crossarms typically have sleeves which are compatible to the boom jibs of derrick and bucket trucks.
Utility companies often find it convenient to string both transmission lines and distribution lines on the same pole or tower. The distribution lines are usually suspended between four to twelve feet below the transmission lines.
This makes it very difficult or impossible to safely raise prior art boom-mounted auxiliary crossarms to a position immediately beneath the transmission lines in order to provide temporary support to the lower mounted distribution conductors.
Another limitation of prior art designs such as that found in applicants U.S. Pat. No. 5,538,207 which issued Jul. 23, 1996, is that they do not permit extensive pivotal movement of the auxiliary crossarm relative to the boom of a service vehicle. A large range of pivotal movement is desirable so that no matter what the orientation of the service vehicle, for example when parked on rough uneven terrain, movement of the auxiliary crossarm easily facilitates simultaneous multiphase conductor capture, and enables insertion of the crossarm between upper and lower-mounted conductors no matter what the angle of the service truck, and to allow for relocation of conductors to different final configurations or different orientations. Fold-down-flat insulators make for compactness, for example when the auxiliary cross-arm is flush down against the boom of transport, and for insertion into tight spacing between existing conductors and crossarms.